The ability to predict an aircraft's trajectory is useful for several reasons. By trajectory, a four-dimensional description of the aircraft's path is meant, for example the three-dimensional position of the aircraft may be specified at each of a series of points in time. The description may be the evolution of the aircraft's state with time, where the state may include the position of the aircraft's centre of mass and other aspects of its motion such as velocity, attitude and weight.
Air traffic management (ATM) would benefit from an improved ability to predict an aircraft's four-dimensional trajectory. Air traffic management is responsible for the safe separation of aircraft, a particularly demanding task in congested airspace such as around airports. ATM decision-support tools based on accurate four-dimensional trajectory predictions could allow a greater volume of aircraft to be handled while maintaining safety.
The ability to predict an aircraft's four-dimensional trajectory will also be of benefit to the management of autonomous vehicles such as unmanned air vehicles (UAVs), for example in programming flight plans for UAVs as well as in commanding and de-conflicting their trajectories.
In order to predict an aircraft's four-dimensional trajectory unambiguously, one must solve a set of differential equations that model both aircraft behaviour and atmospheric conditions. Different sets of differential equations are available for use, some treating the aircraft as a six degrees of freedom of movement system and others treating the aircraft as a point mass with three degrees of freedom of movement. In addition, to solve the equations of motion, information concerning the aircraft's configuration is required as it will respond differently to control commands depending upon its configuration. Hence, further degrees of freedom of configuration may require definition that describe the configuration of the aircraft. For example, three degrees of freedom of configuration may be used to define landing gear configuration, speed brake configuration and lift devices configuration. Accordingly, aircraft intent may need to close six degrees of freedom to define an unambiguous trajectory, three degrees corresponding to motion of the aircraft in three axes and the other three degrees corresponding to aircraft configuration.
The computation process requires inputs corresponding to the aircraft intent, for example an aircraft intent description expressed using a formal language. The aircraft intent description provides enough information to predict unambiguously the trajectory that will be flown by the aircraft. The aircraft intent description is usually derived from flight intent, that is more-basic information regarding how the aircraft is to be flown but that will not provide enough information to allow an unambiguous determination of aircraft trajectory. Aircraft intent may comprise information that captures basic commands, guidance modes and control inputs at the disposal of the pilot and/or the flight management system, and these are expressed as a formal language in the aircraft intent description.
Aircraft intent must be distinguished from flight intent. Flight intent may be thought of as a generalisation of the concept of a flight plan, and so will reflect operational constraints and objectives such as an intended or required route and operator preferences, and may be expressed using a formal language. An instance of aircraft intent provides enough information to indicate how at least one of the aircraft's degrees of freedom is closed, whereas an instance of flight intent does not. For example, an instance of flight intent may correspond to climb from 32000 feet to 38000 feet thus leaving how the climb is performed open, whereas an instance of aircraft intent may correspond to climb from 32000 feet to 38000 feet using a climb rate of 2000 feet per minute.
Flight intent will not unambiguously define an aircraft's trajectory, as it will contain only some of the information necessary to close all degrees of freedom. Put another way, the remaining open degrees of freedom means that there are likely to be many aircraft trajectories that could be calculated that would satisfy a given flight intent. Thus, flight intent may be regarded as a basic blueprint for a flight, but that lacks the specific details required to compute unambiguously a trajectory.
Thus additional information must be combined with the flight intent in order to close all degrees of freedom and to derive the aircraft intent that does allow an unambiguous prediction of the four-dimensional trajectory to be flown. An aircraft intent description that does not close all degrees of freedom is referred to as an open aircraft intent description.
Aircraft intent is expressed using a set of parameters presented so as to allow equations of motion to be solved. The parameters may be left open (e.g. specifying a range of allowable parameters) or may be specified as a particular value. The former is referred to as parametric aircraft intent to distinguish it from the latter where all parameters are specified with particular values that is referred to as fully closed aircraft intent. Thus, an open aircraft intent description may be completed by adding instances of parametric aircraft intent to form a parametric aircraft intent description. The parametric aircraft intent description may then be optimised by determining specific values for each parameter range to form a fully closed aircraft intent description. The theory of formal languages may be used to implement these formulations of aircraft intent: an aircraft intent description language provides the set of instructions and the rules that govern the allowable combinations that express instances of aircraft intent, and so allow a prediction of the aircraft trajectory. Similarly, a flight intent description language may allow instances of flight intent, such as constraints and objectives, to be expressed and to incorporate open aircraft intent descriptions.
EP-A-2040137, also in the name of The Boeing Company, describes aircraft intent in more detail, and the disclosure of this application is incorporated herein in its entirety by reference. EP-A-2482269, also in the name of The Boeing Company, describes flight intent in more detail, and the disclosure of this application is incorporated herein in its entirety by reference.
Currently, existing aircraft antiskid control initialization is optimized for dry runways due to the lack of input to indicate what the runway condition (e.g., the runway coefficient of friction (μ)) may be. This leads to a less than optimized wet/contaminated runway performance because the antiskid control takes longer to get initialized. The present disclosure allows for the selection of the appropriate antiskid control initialization based on the runway condition detected during touchdown/de-rotation of the aircraft.